1. Field of the Invention
The invention relates to an electrode for a power storing apparatus, which used in a power storing apparatus such as a secondary battery or a capacitor, and a power storing apparatus provided with this electrode.
2. Description of the Related Art
An electrode (i.e., a positive electrode or a negative electrode) used in a secondary batter or the like is known in which a uniform electrode layer (i.e., a negative electrode layer or a positive electrode layer) is applied to the entire surface of a collector. However, when the electrode layer is formed on the entire surface of the collector, stress that acts on the electrode, such as stress that is generated when the electrode layer is formed or stress due to vibrations or the like from the outside may cause cracks or the like in the electrode layer.
Japanese Patent Application Publication No. 2005-11660 (hereinafter referred to as “JP-A-2005-11660”) proposes a structure that alleviates stress on the electrode by forming a plurality of minute cells as the electrode layer on the collector. More specifically, a plurality of minute cells are arranged in a matrix at equal intervals on the surface of the collector. On the other hand, Japanese Patent Application Publication No. 2005-71784 (hereinafter referred to as “JP-A-2005-71784”) proposes a structure that uses a plurality of cooling tabs and maximizes the radiation effect of the cooling tabs provided near a center layer in order to suppress variations in temperature between the the center layer side and the outer layer side of a stacked battery.
However, in the electrode for a secondary battery described in JP-A-2005-11660, the intervals between the plurality of minute cells formed on the collector are set evenly, which has the following adverse effects. With a battery having a stacked structure, for example, generated heat during charge and discharge tends to build up in the central portion more so than in the outer peripheral portion of the electrode. When heat builds up in the central portion of the electrode, the internal resistance of the central portion decreases, and as a result, current tends to flow more easily through the central portion. Large amounts of current flowing through the central portion promote heat generation in the central portion so the internal resistance of the central portion decreases even more. As a result, the electrode degrades. Also, for the reason stated above, the temperature distribution on the surface of the electrode is such that the temperature is highest at the central portion and gradually drops toward the outer peripheral side.
Here, JP-A-2005-11660 mentions that the minute cells may be regularly arranged in one region on the collector and irregularly arranged in other regions. However, this structure alone is not enough to uniformly distribute the temperature on the electrode. That is, with the electrode for a secondary battery described in JP-A-2005-11660, the minute cells are not arranged taking the temperature distribution on the electrode into account.
On the other hand, with the stacked battery described in JP-A-2005-71784, for example, the cooling tabs must be provided separately so the number of parts is increased. Also, the structure described in JP-A-2005-71784 changes the radiation effect in the direction of thickness (i.e., in the stacking direction) of the stacked battery, but does not take into account heat radiation based on the temperature distribution in a direction orthogonal to the direction of thickness of the stacked battery (in other words, the in-plane of the collector).